1. Field of the Invention
The present invention relates, generally, to pistons for internal combustion engines. More specifically, the present invention relates to a piston having a patterned coating applied to the piston skirt for directional lubrication flow and/or lubrication retention as well as a method for applying the coating to the piston.
2. Description of the Related Art
Internal combustion engines known in the related art may generally include, among other basic components, an engine block having one or more cylinders, cylinder heads associated with the engine block and pistons supported for reciprocal movement in each cylinder. The piston generally includes a body having a crown and a skirt that depends from the crown to define the bottom half of the body of the piston. The bottom half is referred to as a skirt because it “skirts” or surrounds a pin bore formed in the body. The pin bore corresponds to a similar bore in the connecting rod. A pin is placed through the corresponding bores to attach the piston to the connecting rod.
Generally, fuel is combusted within the cylinders to reciprocate the pistons. The piston drives the connecting rod, which drives the crankshaft, causing it to rotate within the engine block. In this way, power may be translated from the crankshaft to drive an automotive vehicle or any number of other devices. Specifically, the combustion pressure within the cylinder drives the piston downward in a substantially linear motion. In addition to the substantially linear motion of the piston, there is some lateral movement due to the gap (i.e. tolerance) between the outer surface of the piston and the interior wall of the cylinder.
The term “top dead center” refers to the location of the piston at its uppermost point of reciprocal travel relative to the cylinder and is a point at which the piston is at a dead stop or zero velocity. Correspondingly, the term “bottom dead center” refers to the location of the piston at its lowermost point of reciprocal travel relative to the cylinder and is also a point at which the piston is at a dead stop or zero velocity. During movement of a piston from top dead center to bottom dead center on the powerstroke, the angle of the connecting rod produces a force component on the side of the piston commonly referred to as, “major thrust side.” On the other hand, during return movement of a piston from bottom dead center to top dead center produces a force component on the side of the piston commonly referred to as, “minor thrust side.”
As a result of firing pressure acting on the piston within the cylinder, the piston skirt presses against the cylinder wall during the powerstroke and return movement. While lubricant (i.e. oil) generally prevents metal-to-metal contact between the piston skirt and the cylinder wall, factors such a load, temperature and insufficient lubrication may reduce or eliminate the layer of lubricant and cause scuffing on the surface of either the piston skirt or the cylinder or both. Scuffing in this area can ultimately cause the engine to seize or fail.
To reduce the likelihood of scuffing between the piston skirt and cylinder wall, it is well known to provide lubrication between the pistons and cylinder walls. In addition, conventional techniques include coating the piston skirt with a material to assist in lubrication and to avoid metal-to-metal contact between the two components, thereby reducing wear, improving lubrication, and/or thermal properties within the cylinder. The surface of the piston skirt may also be etched or roughed in a random manner to create grooves or depressions, prior to applying the coating, to promote adhesion of the coating material to the surface of the piston skirt. These grooves or depressions also provide areas along the surface of the piston skirt that serve to collect lubrication. Applying a coating in a random manner to reduce scuffing on a piston is generally disclosed in U.S. Pat. No. 3,405,610 issued on Oct. 15, 1968 to H. T. Hill et al.; U.S. Pat. No. 3,935,797 issued on Feb. 6, 1976 to Niimi et al.; U.S. Pat. No. 4,831,977 issued on May 23, 1989 to Presswood; U.S. Pat. No. 5,313,919 issued on May 24, 1994 to Rao et al.; and U.S. Pat. No. 5,884,600 issued on Mar. 23, 1999 to Wang et al.
While coated pistons and/or piston skirts used in connection with internal combustion engines of the type known in the related art alleviate some of the problems associated with insufficient lubrication, high load and temperature during the operation of an internal combustion engine, there remains a need for a coated piston that retains a consistent, uniform layer of lubrication along the outer surface of a piston skirt. In addition, there remains a need for a coated piston that provides a directional lubricant flow pattern to control the distribution of lubricant along the outer surface of the piston/piston skirt.